The present invention relates to split core current transformer.
It is often desirable to monitor power consumption in the individual branch circuits of a facility as well as the overall energy usage by the facility. Individual branch circuit monitoring not only permits billing for energy consumption by the various consumers, but permits billing to be extended to take into account low power factors or high total harmonic distortion, promoting efficiency by allowing the operator of the facility to determine whether and where capital investment for power quality enhancement equipment would provide the best return on investment. Individual branch circuit monitoring can also indicate conditions in the branch circuit, and trigger alerts in case limits on such parameters as RMS voltage or current, power factors, or harmonic distortion are exceeded.
Currents in each of the branch circuits in a facility are typically measured by connecting a current sensor to sense the current flowing in each of the branch power cables exiting the facility's power distribution panel. Generally, a current sensor comprises a sensing transformer installed on an electrical conductor of interest and an electronic circuit that produces an output representative of the electrical current carried by the conductor. The current sensor may be an individual meter for a single circuit or a networked meter that can be temporarily connected, respectively, to each of a plurality of circuits to periodically and momentarily monitor the current in each circuit.
The typical sensing transformer used to sense the electrical current flowing in a power cable comprises a coil of wire wrapped around the cross-section of a magnetically permeable core that encircles the power cable. A sensing transformer with a hinged, split toroidal core is often used because the transformer can be easily affixed to an installed power cable without disconnecting the power cable from a connected device, such as, a circuit breaker in a distribution panel. Cota, U.S. Pat. No. 5,502,374 discloses a split core sensing transformer comprising a toroidal housing divided into a pair of housing halves. Each half of the housing retains a half of the toroidal core of the transformer. The housing halves are interconnected by a hinge located near one end of each half of the housing. The hinge permits pivoting of the housing halves to separate the ends of the housing halves opposite the hinge. The power conductor is passed between the separated ends of the housing halves and the housing halves are then pivoted together encircling the centrally positioned power conductor with the two halves of the toroidal core. On the ends of the housing halves opposite the hinge, a ridge on one housing half and a matching recess on the other half of the housing form a latch to hold the hinged housing halves closed around the power conductor. While the hinged split core sensing transformer permits encirclement of a connected power cable, the resulting current transfer tends to lose its calibration over time.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.